Method and apparatus for effecting gas control in oil wells



June 24, 1969 K. KELLEY 3,451,477

METHOD AND APPARATUS FOR EFFECTING GAS CONTROL IN OIL WELLS Filed June30, 1967 Sheet INVENTOR. KOIZK KELLEY WIM ATTORNEYS K. KELLEY June 24,1969 METHOD AND APPARATUS FOR EFFECTING GAS CONTROL IN OIL WELLS IINVENTOR.

Filed June 30, 1967 United States Patent 3,451,477 METHOD AND APPARATUSFOR EFFECTING GAS CONTROL IN OIL WELLS Kork Kelley, Liberal, Kans.,assignor of one-half to Robert K. Kelley, Fort Worth, Tex.Continuation-impart of application Ser. No. 433,909, Feb. 19, 1965. Thisapplication June 30, 1967, Ser. No. 650,286

Int. Cl. E21b 43/12, 39/00; F04b 21/00 US. Cl. 166-265 11 ClaimsABSTRACT OF THE DISCLOSURE This invention is a continuation-in-part ofmy copending application Ser. No. 433,909, filed Feb. 19, 1965, nowabandoned and relates to improvements in A Method and Apparatus forEffecting Gas Control in Oil Wells. More particularly, this inventionrelates to systems for controlling the rate of production of oil wellswithout wasting gas.

. In many localities, the production of liquid oil and gas from wells isstrictly regulated. Limited production is difficult to obtain withouteffective control over internal well pressure. Moreover, it has beendemonstrated repeatedly that total production from the average well isvery significantly increased where the gas pressure in the formation isretained and utilized instead of being wasted. Efficiency of operationalone is a powerful incentive to accomplish complete gas control, bothas to well pressures and as to conservation of gas energy.

Many efforts have been made to accomplish accurate gas control insidethe well but these attempts have been only partially successful. This ismainly due to a failure to appreciate all of the interacting conditionspresent in the producing zone of the well and resulting failure to solveall of the problems created by such conditions. It should be appreciatedthat the pressures encountered in modern wells, especially those drilledto comparatively great depths, coact with the gas and liquid phases ofthe hydrocarbons encountered to produce conditions which were eitherabsent or much less important in earlier, shallower-wells.

The oil is forced into the well through the rock structure in theproducing formation by gas pressure in the formation higher than thatpresent in the well. This often produces turbulence and foaming withinthe well to such degree that the contents at the producing zone take onmany of the characteristics of a fluid composed of a mixture of liquidand gas, the specific gravity of the fluid depending upon the relativeproportions of each. The apparatus of the present invention isconstructed to provide an environment conducive to the separation of theliquid and gas and is also constructed to provide removal of the liquidfrom the well either by gas pressure alone or gas pressure incombination with pumping. The configuration of the present apparatusalso prevents frac sand and other highly abrasive debris from enteringthe pump string and causing damage to the pump, valves or other parts.The present apparatus is particularly Patented June 24, 1 969 suitablefor use with pumping systems of the character disclosed in United StatesPatent No. 3,324,803, issued June 13, 1967, and entitled, Liquid Controlfor Gas Wells.

In many localities, oil and gas production is strictly limited byappropriate governmental agencies. Most of these agencies limit theproduction per well to as low as 15-25 barrels per day. Many of thewells are capable of producing up to 1,000 barrels per day and it hasbeen the policy in most cases to operate the well long enough each dayto produce the daily allowance and then shut the well down until thenext day. In this procedure, although the flow of oil from the well hasbeen stopped, the gas pressure in the well tends to equalize with thepressure in the surrounding formation. This equalizing of pressureshalts the flow of oil through the formation into the well and the oilwill not move into the bore hole until the gas is vented from the well.The venting of this gas in a relatively short time causes a surgingaction which drives sand, mud and cut oil into the bore and creates afoamy mixture which is difficult if not impossible to pump.

With the use of the gas control system of the present invention, thewell is kept pumping 24 hours a day and positive control is exercisedover the gas pressure in the well so that the daily allowable productionis forced out of the formation into the well during each 24-hour period.This control of pressure in the well provides a stabilized conditionwhich greatly reduces foaming and driving of unwanted debris into thewell bore. Under these conditions, the present apparatus is highlyeffective to permit the pumping of liquid oil out of the well Whileretaining the gas therein.

In wells that are capable of producing a lot of water along with theoil, the action of the present control system in reducing andcontrolling the rate of flow into the well from the surroundingformation often helps greatly in reducing the flow of Water into theWell, probably by reducing surging and allowing natural oilwaterseparation to take place. In addition, it should be clear thatpreventing excessive discharge of gas from the well tends to conservethe reservoir energy stored in the highly compressed gas, and thissaved. energy is available to aid in lifting the oil from the well.

The present invention is adapted to produce oil at a desired rate offlow by controlling gas pressure in the well, so as to produce a desiredquantity of oil during a 24-hour period. This is accomplished bybleeding or metering gas from the interior of the well at a selectedrate of flow through a needle valve, or the like, in such manner thatthe gas pressure in the well controls production of oil from theformation at the desired rate of flow.

The liquid oil and the gas are separated at the bottom of the well,preferably by a positive-action, bucket-type separator, and the oil isremoved from the Well through conventional production tubing. Theseparation of the oil and gas at the bottom of the well, in conjunctionwith the control of the gas pressure in the well, permits the adjustingof the production rate of flow of oil from the well to the desiredamount, Without wasting gas on the one hand or allowing the liquid oilto fill up the bore and choke off the well on the other hand.

Broadly speaking, the liquid-gas separator is responsive to the level ofliquid oil in the well, although it is recognized that foaming andfrothing often occur within wells and it is really a desireddifferential in density of specific gravity which is utilized to controlthe action of the separator. The present invention minimizes surging andconsequent forcing of sand and other unwanted materials into the wellbore. The apparatus is formed in such manner that any sand or otherdebris which might enter the Well bore will be prevented from havingdeleterious effect on the working mechanism or contaminating the oilbeing produced.

Accordingly, it is a principal object of the present invention toprovide a method and apparatus for controlling and conserving gaspressure in oil wells.

Another object of the invention is to provide a method and apparatus foreffecting subsurface gas control in oil wells which will permitcontinuous production of daily allowances through an entire 24-hourperiod and which greatly reduces surging and consequent forcing of sandand other unwanted materials into the well bore.

A further object of the invention is to provide an apparatus of thecharacter described which is formed for removing liquid oil from an oilwell in a condition substantially free from contamination by sand, mudor other debris.

- Yet another object of the present invention is the provision, inapparatus of the character described, of a device responsive to changesin specific gravity of the fluid mixture of liquid oil and gas normallyencountered at the producing zone of an oil well, the device beingeffective for separating the liquid oil from the gas, supplying theliquid oil to a pump string, and returning the gas to the interior ofthe well.

Another object of the invention is to provide apparatus of the characterdescribed which is adapted to function efficiently in wells of greatdepth and under a variety of pressure conditions.

Further objects and advantages of my invention will be apparent as thespecification progresses, and the new and useful features of my Methodand Apparatus for Effecting Gas Control in Oil Wells will be fullydefined in the claims attached hereto.

The preferred forms of the invention are illustrated in the accompanyingdrawings, forming a part of this description, in which:

FIGURE 1 is a fragmentary schematic view of an oil well incorporatingthe apparatus of the present invention;

FIGURE 2 is an enlarged fragmentary view of the upper end of the oilwell of FIGURE 1;

FIGURE 3 is an enlarged vertical cross-sectional view takensubstantially on the plane of 33 of FIGURE 1;

FIGURE 4 is a further enlarged vertical cross-sectional view takensubstantially on the plane of line 44 of FIGURE 3;

FIGURE 5 is a cross-sectional view taken substantially on the plane ofline 5-5 of FIGURE 4;

FIGURE 6 is a cross-sectional view taken substantially on the plane ofline 6-6 of FIGURE 4; and

FIGURE 7 is a cross-sectional view taken substantially on the plane line7-7 of FIGURE 4.

While I have shown only the preferred form of my invention, it should beunderstood that various changes or modifications may be made within thescope of the claims attached hereto without departing from the spirit ofthe invention.

Referring to the drawings in detail, it will be seen that the gascontrol system of the present invention operates to control pressure andconserve gas in an oil well 11 by sealing the upper end 12 of the wellagainst unwanted escape of gas, by venting gas through the sealed upperend of the well at a controlled rate to lower the gas pressure withinthe well sufficiently to cause the desired quantity of oil to be forcedinto the well from the surrounding formation 13, by separating theliquid oil from the gas within the well, and by thereafter removing theliquid oil from the well.

The apparatus for accomplishing this is adapted for use in theconventional Well casing 14 positioned in the bore hole 15 and the usualpump string 16 mounted in the casing with its lower end in communicationwith the producing zone of the well and its upper end 17 passing througha gas tight sealing device 18 secured to the upper end of the wellcasing 14. It should be understood that the casing 14 may be positionedin the well in any of a number of conventional ways, the main essentialbeing that the well bore is normally sealed against the escape of gasand consequent drop in gas pressure.

Means 19 is provided for venting gas from the well at a controlled rateof flow so as to lower the gas pressure within the well comparativelyslowly and only by an amount sufficient to accomplish the purpose of thepresent invention. The slowness of the drop in pressure prevents surgingwhich ordinarily causes excessive foaming and carrying of sand, mud andother debris into the interior of the well casing. The controlledventing of the gas permits the operator to attain a drop in pressurewhich is just enough to accomplish continuous and relatively non-surgingflow of oil from the surrounding formation into the well casing inamounts equal to the permitted production rate of the well over a24-hour period.

The means 19 may be located in any suitable place to accomplish thedescribed controlled venting of gas from the well, but preferably ismounted above ground at the casing head, Christmas tree, or otherstructure used to seal the well. As here shown, the means 19 consists ofa conventional needle valve mounted on the seal 18 in communication withthe interior of the well casing. While a needle valve is preferred, itshould be apparent that any other suitable means for accomplishingcontrolled venting of gas from the well at a desired rate of flow couldbe used.

In accordance with the present invention, and referring specifically toFIGURES 3-7 of the drawings, it will be seen that the liquid oil isseparated from the gas and supplied to the pump string 16 by apparatuspositioned within the well casing at the producing zone. As here shown,this apparatus includes valve means 21 positioned at the lower end ofthe pump string 16 and formed for selectively communicating the interiorof the pump string with the interior of the well casing, together withcontrol means 22 responsive to changes in the specific gravity of thefluid mixture, usually liquid oil and gas, encountered at the producingzone of the well, the control means 22 having an operative connection tovalve means 21 formed for opening and closing the latter in accordancewith the rise and fall of the said specific gravity, so as to supplyliquid oil only to the pump suction line.

As here shown, the control means 22 includes an open top cylindricalbucket 23 formed for vertical reciprocation within the well and having aweight suflicient to pull the valve means 21 to open condition againstthe gas pressure in the Well when the bucket is only partly filled.Thus, as liquid oils cascade into the bucket through its open top, thecombined weight of oil and the bucket will open the valve means 21 andprovide access for the liquid oil to the pump string.

The bucket 23 is formed and proportioned to provide an effectivedisplacement sufficient to float the bucket in the surrounding fluidmixture when the bucket is substantially empty of liquid oil, thefloating action being sufiicient for urging the valve means 21 to closedcondition. Thus, so long as liquid oil is available in the bucket, thevalve means 21 will remain open, but as the amount of liquid oil in thebucket is depleted, the bouyancy of the bucket will cause the valvemeans 21 to close before any gas can enter the pump string. Thisprevents gas lock and ensures that gas will not be discharged from thewell through the pump string even if mistakes are made by the operatorsabove ground level.

As may best be seen in FIGURE 4 of the drawings, the valve means 21 isof the valve-on-valve type in order to reduce the bucket weightnecessary to open the valve means, thus also reducing the length ofbucket necessary to provide the described flotation displacement.Accordingly, valve means 21 includes a main valve member 20 moveablevertically toward and away from a valve seat 24 provided by the lowerend of a nipple 26 threadably secured to and communicating with thelower end of the pump string 16. The main valve member 20 is formed witha central opening 27 extending axially therethrough, opening 27 being ofconsiderably smaller cross-sectional area than the opening in nipple 26surrounded by seat 24.

The valve means 21 also includes a secondary valve member 28 mounted forvertical movement toward and away from a valve seat 29 formed around thelower end of opening 27 in main valve member 20. Secondary valve member28 is operatively connected to bucket 23 by a rod 31 so it will move upand down with the rise and fall of the bucket. This up-and-down movementis guided by a vertically elongated cage 32 which is threadably securedto main valve member 20. As the secondary valve member 28 movesdownwardly away from its seat 29 under the influence of the weight ofthe bucket 23, it encounters a ring member 33 secured to the lower endof cage 32 in closely surrounding relation to rod 31 so that the weightof the partially-filled bucket 23 will be transferred to the main valvemember 20 as the bucket continues to descend.

The pressure drop across valve means 21 can be very considerable whenworking with very deep wells or wells having high gas pressures. Inorder to bodily pull the main valve open under these conditions, thebucket would have to be unnecessarily heavy and, accordingly,unnecessarily long. With the structure described, much less weight isrequired to pull the secondary valve member from its seat and thispermits liquid to flow from the well into the pump string, greatlyreducing the amount of pressure drop across the main valve. Thus, whenthe lost motion connection provided by the secondary valve member 23engaging ring 33 transfers the Weight of the partially-filled bucket tothe main valve, such weight will be suflicient to pull the main valvemember 20 from its seat 24. When the supply of liquid oil in the bucketis substantially depleted, the bucket will float upwardly and urgesecondary valve member 28 against its seat. This, in turn, will urgemain valve member 20 to closed condition against its seat 24, thusclosing oif the pump string 16 from the well and preventing the entry ofgas from the well into the pump string.

The structure of the valve means 21 and control means 22 thus fardescribed is basically similar to the structure of the oil-gas separatordisclosed in my Patent No. 2,291,902, issued Aug. 4, 1942 and entitledGas Anchor. While the device shown in that patent might work effectivelyin some wells, if substituted for the apparatus illustrated in FIGURES3-7 of the present drawings, the present apparatus contains severalfeatures of novelty which provide fool-proof operation in a greatvariety of wells under a great variety of conditions. Accordingly, it ispreferred that the gas-oil bottom hole separating device shown anddescribed herein be used in my gas control system.

In accordance with the present invention, and as a valuable featurethereof, the valve means 21 and control means 22 of the presentinvention are formed and mounted in such a way as to ensure thatsubstantially uncontaminated liquid oil is the only material allowed topass through the valve means 21 and enter the pump string 16. The valueof this accomplishment should be apparent when it is realized thatcontaminants and debris such as sand, mud, rock chips and the likenormally found in oil wells are all highly abrasive and could causeexcessive wear to the valve structures as well as to the pumpsusuallyemployed for lifting the oil out of the well.

In the present invention, most of the debris are prevented from enteringthe bucket 23, and those that do enter are trapped in the bucket and donot pass through the valve means 21 into the pump string 16. Preventingalmost all of the debris from entering bucket 23 is accomplished byrouting the flow of fluid upwardly through an annular space between thebucket 23 and the bellshaped skirt 34 mounted in surrounding relationthereto. As here shown, skirt 34 is provided as a downward extension ofa tubular member 36 carried on the lower end of pump string 16 insurrounding relation to an elongated cylindrical housing 37, alsocarried by the lower end of pump string 16. With this construction, thefluid mixture of gas and oil passes downwardly between the skirt 34 andwell casing 14, then makes a degree bend to enter the open bottom ofskirt 34 and pass upwardly through the annular space 38 between skirt 34and bucket 23. Since the bucket 23 and skirt 34 may be as much as 30 or40 feet long, depending upon weight and flotation characteristicsrequired of the bucket, and because of the abrupt 180 degree bendrequired, most of the unwanted debris 39 drop down to the bottom of thewell and are not carried up through annular space 38. The latter spacealso serves to reduce the foaming effect and promote separation of thegas from the liquid oil. Once the liquid oil level reaches the open top41 of the bucket 23, it cascades down into the bucket. As the bucketfills, its buoyancy is reduced and eventually the combined weight ofbucket and oil causes the bucket to sink down and pull the valve means21 to open condition.

Trapping of any minor amounts of debris which might have been carriedinto the bucket is effected by mounting the valve means 21 in spacedrelation above the bucket and extending a tubular probe member 42downwardly from the housing 37 in concentrically spaced relation aroundthe rod 31 and with its lower end 43 terminating at short distance abovethe bottom 44 of the bucket when the latter is in its uppermostposition, From FIGURE 3 of the drawing, it may be seen that the probe 42not only provides a conduit for the liquid oil. to pass from the bucket23 upwardly through the valve means 21 and into pump string 16, but alsoserves as a guide for the rod 31.

In operation, needle valve 19 is opened sufiiciently to bleed oif enoughgas from the interior of the well to cause a slight pressure dropsuflicient for the reservoir gas pressure to urge the desired quantityof oil through the formation and through the usual holes 46 into thewell casing 14. As the specific gravity of the fluid mixture in thebucket increases, due to an increasing percentage of liquid oil, thebuoyancy of the bucket will be reduced and it will eventually sink downfar enough to pull valve means 21 to open condition. So long as liquidoil is being supplied to the bucket as fast or faster than it is beingremoved through the pump string 16, the apparatus will remain in thedescribed condition. As soon as the specific gravity of the mixturedrops, due to the depletion of the amount of liquid oil in the bucket23, buoyancy will be reestablished and the bucket will rise so as toclose the valve means 21 before the probe 42 starves for oil andunwanted gas enters the pump string.

Preferably, the needle valve is adjusted so that the well will flow onlya small quantity of the oil that would otherwise flow with full venting.Generally, this small quantity will be equal to that allowed byappropriate governmental agencies and will be less than, say, two orthree percent of the production which would be possible on full venting.In this way, the pressure within the gas casing is retained at such ahigh degree that volatile components do not come out of the solution inthe producing zone at an undue rate. In this way, more produceableliquids flow into the well and considerably greater overall productivityis achieved from the well.

In conclusion, it should be noted that the method and apparatus of thepresent invention is effective for use in wells in which gas pressurealone is relied upon to force the liquid from the well. However, in. thegreat majority of wells, some type of pumping means is normallyemployed. Any suitable pumping means may be used which can accommodateclosing of the valve means 21 during the periods when no liquid oil isavailable for pumping. Many such pumping devices are well known in theoil well industry.

From the foregoing, it will be seen that I have provided a novel andefficient gas control system for controlling gas pressures within thewell, regulating oil production, and

7 furnishing relatively uncontaminated oil to the pump string.

I claim:

1. The method of producing an oil well having a well casing andproducing line and removing a desired quantity of liquid oil therefromper day comprising sealing the well casing against unwanted escape ofgas therefrom, controlling the gas pressure in the well casing byventing gas from the well casing at a controlled substantially uniformrate to keep the gas pressure within the well at a level just suflicientto cause oil to be forced into the well from the surrounding formationat a desired rate of production, effecting separation of the liquid oilfrom the gas at the bottom of the well in response to the level of theoil in the well, and removing the separated liquid oil from the wellthrough the producing line.

2. The method as described in claim 1 and wherein said controlling ofgas pressure within the well is accomplished by metering gas from thewell through a needle valve at the upper end of the well.

3. Apparatus for producing an oil well while controlling pressure andconserving gas therein, comprising a well casing positioned in the boreof an oil well and having a gas tight seal at the upper end thereof,venting means in the gas tight seal for venting selected amounts of gasfrom said casing at a substantially uniform rate so as to preventexcessive increase of pressure in the casing, and maintain the casingpressure at a desired level, a pump string mounted in said casing-andhaving a lower end in communication with the producing zone of the welland an upper end passing through said gas tight seal in the upper end ofsaid casing, pump means connected to said pump string and formed forproducing a lowered pressure therein for drawing liquid oil out of saidwell, valve means at said lower end of said pump string formed forselectively communicating the interior of said pump string with theinterior of said casing, and control means inside said casing at theproducing zone of the well and responsive to changes in specific gravityof the fluid mixture encountered thereat, said control means having anoperative connection to said valve means formed for opening and closingthe latter in accordance with the rise and fall of the said specificgravity so as to supply liquid oil only to the pump suction line.

4. Apparatus for producing an oil well having a pump and pump suctionline while effecting gas control therein, comprising a well casingpositioned in the bore of an oil well, a gas tight seal at the upper endof said casing, a control valve in the gas tight seal for ventingcontrolled amounts of gas from said casing at a substantially uniformrate so as to maintain the pressure in the casing at a desired level,and separating means for separating oil and gas in the producing zone ofthe well; said separating means comprising valve means adapted forconnection to the intake end of the pump suction line, and control meansadapted for positioning at the producing zone of the oil well andresponsive to changes in specific gravity of the fluid mixtureencountered thereat, said control means having an operative connectionto said valve means formed for opening and closing the latter inaccordance with the rise and fall of the said specific gravity so as tosupply liquid oil only to the pump suction line.

5. Apparatus as described in claim 4, in which the control valve in thegas tight seal is a needle valve.

6. In a system for eifecting gas control in an oil well, an apparatusfor separating oil and gas in the producing zone of the well, comprisinga main valve providing a main valve member moveable vertically towardand away from a valve seat adapted for connection to the intake end of apump suction line, said main valve member being formed with an openingtherethrough of smaller crosssectional area than said seat of said mainvalve, a secondary valve providing a secondary valve member moveablevertically toward and away from a valve seat formed around said openingthrough said main valve member,

an open top bucket formed for vertical reciprocation within the well,with its open top a spaced distance below said main valve, meanscommunicating said main and secondary valves with the interior of saidbucket, a rod secured to the bottom of said bucket and said secondaryvalve member, and a lost motion connection between said main valvemember and said secondary valve member, said bucket having a weightsufiicient to pull said secondary valve member from its seat against thegas pressure in the well when said bucket is partially filled withliquid so as to reduce the pressure drop across said main valve, saidlost motion connection being formed for pulling said main valve from itsseat after said secondary valve is opened, said bucket having aneffective displacement suflicient to float said bucket in thesurrounding fluid mixture when said bucket is substantially empty ofseparated liquid so as to urge said main and secondary valve membersagainst their respective seats.

7. An apparatus as described in claim 6 and wherein an elongatedcylindrical housing is mounted in enveloping relation around said mainand secondary valves, and a tubular probe member extends downwardly fromsaid housing in concentrically spaced relation around said rod andterminates adjacent to the bottom of the said bucket when the latter isin its uppermost position for guiding said rod and providing said meansand communicating said valves in the interior of said housing with theinterior of said bucket near the b ottom thereof.

'8. An apparatus as described in claim 7 and wherein a tubular memberhaving an elongated bell-shaped skirt open at the bottom is mounted inconcentrically spaced relation around said bucket and cooperatestherewith to define an annular passage whereby the fluid mixture fromthe well enters the open bottom of said bell-shaped skirt and passesupwardly through said annular space and into the open top of the bucketwhereby sand and other unwanted debris will drop into the bottom of thewell and will not be carried into the bucket with said fluid mixture.

9. Apparatus for producing an oil well having a pump and pump suctionline while effecting gas control therein, comprising a well casingpositioned in the bore of an oil well, a gas tight seal at the upper endof said casing, a control valve in the gas tight seal for ventingselected amounts of gas from said casing so as to reduce the pressure inthe casing by a desired amount, and separating means for separating oiland gas in the producing zone of the well; said separating meanscomprising valve means adapted for connection to the intake end of thepump suction line, and control means adapted for positioning at theproducing zone of the oil well and responsive to changes in specificgravity of the fluid mixture encountered thereat, said control meanshaving an operative connection to said valve means formed for openingand closing the latter in accordance with the rise and fall of the saidspecific gravity so as to supply liquid oil only to the pump suctionline, said control means also having an open-top bucket formed forvertical reciprocation within the well, said bucket having a weightsufficient to pull said valve means open against the gas pressure in thewell when said bucket is partially filled and having an effectivedisplacement suflicient to float said bucket in the surrounding fluidmixture when said bucket is substantially empty for urging said valvemeans closed.

10. An apparatus as described in claim 9 and wherein a tubular memberhaving an elongated bell-shaped skirt open at the bottom is mounted inconcentrically-spaced relation around said bucket in such manner thatthe fluid mixture from the well enters the open bottom of the skirt andpasses upwardly through the annular space between said bucket andbell-shaped skirt and into the open top of the bucket whereby sand andother unwanted debris will drop into the bottom of the well and will notbe carried into the bucket with said fluid mixture.

11. An apparatus as described in claim 10 and wherein said tubularmember extends vertically above the open 9 10 top of said bucket and isformed with an opening there- 2,905,246 9/ 1959 Rodgers 166-54 throughfor venting gas trapped in the upper part of said 3,045,751 7/ 1962Rodgers 16654 tubular member back into the well. OTHER REFERENCES e e cCited Uren, Lester C., Petroleum Production Engineering: UNITED STATES PT Oil Field Exploitation, New York, McGraw-Hill, 3rd Ed.,

M- Pendleton I L E 1,431,777 10/1922 Conrader 166- -6 CH ES E L 21234753/1938 Rodgers 5 10 I. A. CALVERT, Assistant Exammer. 2,142,376 1/1939Rodgers 166541 2,291,902 8/1942 Kelley 1- 10340 2,370,296 2/1945Ehretsman et al 137-191 103-203; 13719l; 166-54, 68, 314

